This invention is generally directed to liquid developer compositions and, in particular, to liquid developers comprised of a mixture of high and low vapor pressure fluids, and wherein there is enabled with such developers in embodiments excellent fixing characteristics especially when the developed image is transferred from an intermediate substrate to the final substrate, such as paper, reference for example U.S. Pat. No. 5,276,492, the disclosure of which is totally incorporated herein by reference. In embodiments of the present invention there is provided developers and processes for achieving high fix wherein the developers contain a high vapor pressure fluid, such as an Isopar, like ISOPAR L.RTM., and a low vapor pressure fluid, such as NORPAR 15.RTM., SUPURLA NF5.RTM., and the like, and which low vapor pressure fluid is substantially odorless. The high vapor pressure fluid in embodiments is removed by heat once the developer is transferred to the intermediate substrate, and the low vapor pressure fluid remains with the developer when the developed image is transfixed, that is transferred, fixed and heated simultaneously, to a supporting substrate like paper. Poor or unacceptable transfer can result in, for example, poor solid area coverage if insufficient toner is transferred to the final substrate and can also lead to image defects such as smears and hollowed fine features. To overcome or minimize such problems, the liquid toners of the present invention were arrived at after extensive research efforts, and which toners result in, for example, sufficient particle charge for transfer and maintain the mobility within the desired range of the particular imaging system employed.
A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. The aforementioned dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are also known for forming latent electrostatic images such as, for example, providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. After the latent image has been formed, it is developed by colored toner particles dispersed in a nonpolar liquid. The image may then be transferred to a receiver sheet.
Useful liquid developers can comprise a thermoplastic resin, pigment, and a dispersant nonpolar liquid. The colored toner particles are dispersed in a nonpolar liquid which generally has a high volume resistivity in excess of 109 ohm-centimeters, a low dielectric constant, for example below 3.0, and a high vapor pressure. Generally, the toner particles are less than 10 microns in diameter as measured with the Horiba Capa 700 Particle Size Analyzer.
Since the formation of proper images depends, for example, on the difference of the charge between the toner particles in the liquid developer and the latent electrostatic image to be developed, it has been found desirable to add a charge director compound and charge adjuvants which increase the magnitude of the charge, such as polyhydroxy compounds, amino alcohols, polybutylene succinimide compounds, aromatic hydrocarbons, metallic soaps, and the like to the liquid developer comprising the thermoplastic resin, the nonpolar liquid and the colorant.
U.S. Pat. No. 5,019,474 the disclosure of which is hereby totally incorporated herein by reference, discloses a liquid electrostatic developer comprising a nonpolar liquid, such as the Isopars, thermoplastic resin particles, and a charge director. The ionic or zwitterionic charge directors may include both negative charge directors such as lecithin, oil-soluble petroleum sulfonate and alkyl succinimide, and positive charge directors such as cobalt and iron naphthanates. The thermoplastic resin particles can comprise a mixture of (1) a polyethylene homopolymer or a copolymer of (i) polyethylene and (ii) acrylic acid, methacrylic acid or alkyl esters thereof, wherein (ii) comprises 0.1 to 20 weight percent of the copolymer; and (2) a random copolymer of (iii) vinyl toluene and styrene and (iv) of butadiene and acrylate. As the copolymer of polyethylene and methacrylic acid or methacrylic acid alkyl esters, NUCREL.RTM. may be selected.
U.S. Pat. No. 5,030,535 discloses a liquid developer composition comprising a liquid vehicle, a charge control additive and toner particles. The toner particles may contain pigment particles and a resin selected from the group consisting of polyolefins, halogenated polyolefins and mixtures thereof. The liquid developers are prepared by first dissolving the polymer resin in a liquid vehicle by heating at temperatures of from about 80.degree. C. to about 120.degree. C., adding pigment to the hot polymer solution and attriting the mixture, and then cooling the mixture so that the polymer becomes insoluble in the liquid vehicle, thus forming an insoluble resin layer around the pigment particles.
Moreover, in U.S. Pat. No. 4,707,429 there are illustrated, for example, liquid developers with an aluminum stearate charge additive. Liquid developers with charge directors are also illustrated in U.S. Pat. No. 5,045,425. Further, stain elimination in consecutive colored liquid toners is illustrated in U.S. Pat. No. 5,069,995. Additionally, of interest are U.S. Pat. Nos. 4,760,009; 5,034,299 and 5,288,508.
The disclosures of each of the U.S. Patents mentioned herein are totally incorporated herein by reference.
In U.S. Pat. No. 5,306,591 and U.S. Pat. No. 5,308,731, the disclosures of which are totally incorporated herein by reference, there is illustrated a liquid developer comprised of a nonpolar liquid, thermoplastic resin particles, a nonpolar liquid soluble ionic or zwitterionic charge director, and a charge adjuvant comprised of an aluminum hydroxycarboxylic acid, or mixtures thereof.
In copending U.S. patent application Ser. No. 08/357,471, the disclosure of which is totally incorporated herein by reference, there is illustrated a liquid developer comprised of a nonpolar liquid, thermoplastic resin particles, polar organic additives with a dielectric constant in the range of about 20 to about 150, and soluble in the nonpolar liquid; and charge director. A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. Examples of liquids illustrated in the aforementioned copending application include the ISOPAR.RTM. series (manufactured by the Exxon Corporation), the NORPAR.RTM. series available from Exxon Corporation, the SOLTROL.RTM. series available from the Phillips Petroleum Company, and the SHELLSOL.RTM. series available from the Shell Oil Company.